There have been construction machines that use a cooling circuit which cools an electric motor thereof with the use of cooling fluid (see, for example, Patent Literature 1). In such a cooling circuit, cooling fluid is supplied from a pump to an electric motor. Then, the cooling fluid circulates in the electric motor so as to cool the electric motor. After cooling the electric motor, the cooling fluid flows out of the electric motor, and is cooled by a heat exchanger such as a radiator. Then, the cooling fluid is supplied again to the electric motor.
Generally, for cooling an electric motor for a construction machine, cooling fluid that has been filtered by a filter is circulated within the electric motor. Since foreign objects are removed from the cooling fluid by the filter, entry of the foreign objects into the electric motor is prevented.